1. Technical Field of the Invention
The present invention relates in general to Ethernet Operations, Administration and Management (OAM), and in particular, to Connectivity Fault Management (CFM) in Ethernet OAM.
2. Description of Related Art
Ethernet OAM provides protocols for installing, monitoring and troubleshooting Ethernet metropolitan area networks (MANs) and Ethernet wide area networks (WANs). Several different standards bodies have developed working protocols for Ethernet OAM. For example, the Institute of Electrical and Electronics Engineers (IEEE) has produced the IEEE 802.1ag standard, which defines Connectivity Fault Management (CFM) in enterprise and carrier networks. Similarly, the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) has produced the Y.1731 standard, which defines both fault management and performance monitoring in carrier networks.
The IEEE 802.1ag standard further partitions the network into hierarchical maintenance domains (MDs) and defines roles for maintenance endpoints (MEPs) and maintenance intermediate points (MIPs) within each domain. For example, a customer (higher) level domain includes maintenance endpoints (MEPs) within customer premises equipment and maintenance intermediate points (MIPs) within provider edge switches and core operator switches, while a provider (lower) level domain includes MEPs within provider edge switches and MIPs within core operator switches. Thus, the lower level domain MEPs are nested with the higher level domain MIPs within the provider edge switches.
Currently, the Ethernet OAM Protocol, as described in the IEEE 802.1ag standard and similarly described in the ITU-T Y.1731 standard, includes the following primitives: Fault Detection, Fault Verification and Fault Isolation. Fault Detection is supported using CFM Continuity Check Messages (CCMs), which are “heartbeat” messages issued periodically by maintenance endpoints (MEPs) in the network. CCMs allow MEPs to detect loss of service connectivity amongst themselves, enable MEPs to discover other MEPs within an Ethernet maintenance domain (MD) and enable maintenance intermediate points (MIPs) to discover MEPs.
Fault Verification is supported using CFM Loop-Back messages, which are transmitted by MEPs at the request of an administrator to verify connectivity to a particular maintenance point (MEP or MIP). Fault Isolation is supported using link trace messages, which are transmitted by a MEP at the request of an administrator to track the path (hop-by-hop) to a destination MEP. Link trace allows the transmitting MEP to discover connectivity data about the path.
The increasing deployment of Carrier Ethernet in metropolitan areas, such as residential complexes, shopping malls and small businesses, has created several challenges for service providers. To facilitate Metro Ethernet services to customers, service providers have been installing pure Ethernet-based devices on-site as customer premises equipment (CPE). With the proliferation of these Ethernet-based devices, the scalability of Ethernet OAM (especially in the higher customer domains) has become an issue. In particular, since IEEE 802.1ag has recommended using CFM as a base primitive to support Fault Detection, the increasing deployment of Carrier Ethernet in Metro networks has resulted in an increased number of CFM frames traversing the Metro cloud and an increased cost and complexity of Ethernet-based CPE due to the required hardware and software necessary to support the CFM traffic. The high cost of such Ethernet-based CPE necessarily increases the overall cost of deployment.
To reduce the cost, a Metro Ethernet service provider may desire to support only Fault Verification and Fault Isolation, but not Fault Detection, since the Fault Detection primitives (e.g., CCM) have substantial overhead, and therefore do not scale well. However, the current standard for Ethernet OAM in IEEE 802.1ag and ITU-T Y.1731 requires service providers to implement Fault Detection in Metro networks. Therefore, what is needed is an enhancement to Ethernet OAM to reduce the cost and complexity of running CFM in Metro networks.